The present invention relates to apparatus for cooling strip metal, for example, during passage of the strip through a continuous annealing line, galvanizing line, or the like.
A typical known arrangement for the continuous cooling of strip metal processed in a continuous annealing furnace, or the like, is schematically shown in FIG. 1(a). Thus, strip metal 2 is fed around a plurality of spaced cooling rolls 1 so that the strip is cooled at the areas in contact with these cooling rolls, while passing therethrough. These cooling rolls 1 are, as typically shown in FIG. 1(b), of such a construction that they are rotatably supported on bearings 3, and have a helical or spiral passage 5 formed in the radially inner surface of a shell 4, around the outer surface of which the strip 2 passes in contact relationship. A pair of rotary coupling joints 6 are provided, adapted to inter-communicate with the mentioned spiral passage 5 via a rotating shaft 7, and through which cooling water is fed into the spiral passage 5 for cooling the shell 4. The number of cooling rolls 1 may vary depending upon the amount of cooling required of the strip.
With such conventional cooling arrangements, a drawback has been found due to occasional irregularities or distortions in the general configuration of the strip metal. More specifically, it is known that configurational distortions of the strip are attributable to certain irregular thermal stresses as a result of occassional deviations in temperature distribution widthwise of the strip. Such uneven temperature distribution can be caused by uneven contact of the strip with the surfaces of the cooling rolls, e.g. due to biased or uneven stretching existing in the strip. Also, the extent of such uneven widthwise temperature distribution could increase as the cooling rate of the strip per pass through a cooling roll increases. As a consequence, it is possible in practice to prevent such distortions of the strip from occurring, if the cooling rate of the strip metal per pass of a roll is limited to a range which ensures that no distortions of the strip can occur; however, this limitation causes a further problem, which is attributable to the conventional use of water as coolant for the cooling rolls, as follows:
It is normal practice for controlling the cooling effect rendered upon the strip metal, that the volume of water passing through the cooling rolls can be changed, and that the temperature of the cooling water be changed; this, however, causes the following problem, i.e., in the case that the volume of water is decreased at a time when the temperature of the strip is high, the cooling water could possibly be vaporized, which would then cause an occasional mismatching in the cooling effect widthwise of the strip. On the other hand, if the temperature of the cooling water is high, again there could be the possibility of the cooling water boiling or vaporising, thereby to cause uneven cooling widthwise of the strip. Worse still, it is to be noted that the range of control of the cooling rates attainable from such an arrangement would be substantially small, i.e. the volume of cooling water cannot be decreased significantly in view of the possibility that it will boil or vaporize, and with a change of water temperature say from 20.degree. to 90.degree. C., the control range attained at a strip temperature of around 800.degree. C. could be as small as 10% or so; even with a strip temperature of 400.degree. C., the control range would be merely 20% or so.
Therefore, the typical arrangement for cooling strip metal as discussed above, is such that the angle of contact, and hence the area of contact between the strip and the cooling roll shells must be adjusted; this is effected in practice mostly from a change in the cooling roll positions. However, if a change of cooling roll positions to achieve a required cooling capacity is effected on every occasion that the material and thickness of strip and the running velocity of the strip cooling line is changed, this could substantially affect the parallelism between adjacent pairs of cooling rolls. This would then be not only a cause of mistracking or zig-zag running of the running strip, but also a further cause for unbalanced contact between the strip and the cooling rolls.